Procedure for determining the dynamic behavior of a vehicle on a test bench

ABSTRACT

A method for measuring the displacement of a vehicle wheel relative to the frame thereof or relative to a fixed point of reference. The vehicle is located on a test stand in which the wheel is loaded, statically or dynamically. In a first step, a measuring system including cameras measures the position of at least three points of reference on the wheel, these three points of reference not being in a straight line. In a second step, the relative displacement of the wheel is calculated.

FIELD OF THE INVENTION

The invention relates to a method for measuring the displacement of awheel of a vehicle relative to the frame thereof or relative to a fixedpoint of reference, when this vehicle is located on a test stand, inwhich the vehicle, preferably via the said wheel is loaded, staticallyor dynamically.

BACKGROUND OF THE INVENTION

According to the present state of the art, such measurements are takenusing linear inductive wheel motion recorders, laser projection sensorsor milometers on the basis of unwinding reels of cord in conjunctionwith a rotary encoder.

All these commonly-used measuring systems and the test methods have thedrawback that only a limited excitation of the wheel can be measured.Hence, on account of the technical features of the existing measuringsystems, only a maximum rotation or inclination of the wheel in theregion of 20 degrees can be measured. In addition, these existingsystems are no good for taking measurements if and when the wheel isloaded at a frequency which is higher than 10 Hz or if this wheel issubjected to large excitations.

These existing test set-ups are extremely complex in their design, hardto calibrate and it is, on top of that, very laborious to build inadditional points of reference on the frame.

SUMMARY OF THE INVENTION

The aim of the method, according to the invention, is to remove thesedrawbacks and to propose a method which allows measurements to be takenat very high frequencies and with very large displacements of the wheelrelative to the frame. With this method it is also possible to measurevery large rotations or inclinations of the wheel.

In addition the method, according to the invention, offers the addedadvantage that, in a straightforward way, a high number of extra pointsof reference can be incorporated in the frame. These points of referencecan be depicted in a shared system of coordinates relative to one andthe same coordinate system.

To this aim, in the method according to the invention, in a first step,the position of at least three, not lying in a straight line, points ofreference on the said wheel are measured by means of a measuring systemwhich, preferably, comprises linear cameras or matrix cameras, in whichsubsequently, in a second step, the said relative displacement iscalculated.

To this end, prior to the first step, the said wheel is subjected to arevolution about the axis of rotation thereof while successive positionsof at least one of the points of reference are measured on the thus,through the point of reference under consideration, traced arc, inwhich, on the one hand, a plane is defined which is parallel to this arcand, on the other hand, the centre of the circle on which the arc liesand which lies on the said axis of rotation is calculated, so as todetermine a coordinate system whose first axis coincides with the axisof rotation and a second and third axis lie in the said plane.

In a preferred embodiment of the method, according to the invention, thesaid coordinate system is displaced along the direction of the axis ofrotation over a known distance such that the said plane coincides withthe median transverse vertical plane of the wheel.

According to a special embodiment of the method, according to theinvention, the position of the points of reference of several wheels ofthe said vehicle in a state of rest is determined relative to oneanother such that the positions of these points of reference can beexpressed in terms of one and the same coordinate system.

Other peculiarities and advantages of the invention will soon becomeapparent from the following description of a specific embodiment of themethod and the configuration according to the invention; thisdescription is only given as an example and does not limit the scope ofthe protection that is being claimed; the reference numbers usedhereinafter bear upon the figures appended hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective drawing of part of a test standshowing part of a vehicle.

FIG. 2 is a schematic representation of a wheel with three points ofreferences in side elevation.

FIG. 3 is a schematic representation of the wheel out of FIG. 2 viewedend-on.

FIG. 4 is a schematic top view of a test stand with a vehicle on it.

In the various figures, the same reference numbers bear upon the same oranalogous elements.

In the method, according to the invention, a vehicle, e.g. a car, ofwhich, for example, the wheel suspension is to be tested, is set upon atest stand. This test stand is equipped with actuators which mean thatat least one wheel of the vehicle can be exited such that the wheel issubjected to a translatory movement and/or a rotation.

Represented schematically, in FIG. 1, is such an actuator 1 on which awheel 2 rests of a vehicle 3.

In the method, according to the invention, three points of reference 4and fitted to the side surface of the wheel 2. These points of reference4 consist of light-emitting diodes (LEDs). Also mounted on the frame 5of the vehicle 3 are three points of reference 6 each of which, likebefore, consists of a light-emitting diode (LED).

DETAILED DESCRIPTION OF THE INVENTION

After that, the said actuator 1 is activated and a specified excitationis imposed on the wheel 2.

In order to determine the displacement of the wheel 2 relative to theframe 5 of the vehicle 3, are measured, in a first step, using ameasuring system 7, which comprises three linear cameras 8, the positionof the points of reference 4 of the wheel 2 and the points of reference6 of the frame 5.

The use of a measuring system 7 with linear cameras 8 means that theposition of the points of reference 4 and 6 can be measured at very highspeed and with great precision, such that measurements can be carriedout for excitations of the wheel 2 at frequencies up to 500 Hz. Theselinear cameras 8 make it, for instance, possible to operate at 3,000measurements per second.

Such a high-frequency measuring system is, in itself, well-known and ananalogous measuring system was set down in the Belgian patentapplication No. 09700143.

Starting from each position thus measured for the three points ofreference 4 of the wheel 2 and for the three points of reference 6 ofthe frame 5 is then calculated, in a second step, the displacement ofthe wheel 2 relative to the frame 5 using already well-documentedtrigonometry.

In an alternative embodiment of the method, according to the invention,the displacement of the wheels 2 and the frame 5 are determined relativeto a fixed point of reference, for example the test stand itself.

In a preferred embodiment of the method, according to the invention, isset up, prior to the above-mentioned first step, a coordinate systemwhich is fixed with respect to the wheel 2, whose displacement relativeto the frame 5 is to be determined.

Firstly, to that end, a plane is determined which is perpendicular tothe axis of rotation of the wheel 2 in question and, after that, acentre of rotation of this axis of rotation is calculated. In this waythe axis of rotation itself of the wheel 2 can be calculated exactly asthis axis is at right angles to the said plane and runs through thecentre of rotation.

In a first variant on the method are measured, for the determination ofthis plane, by means of the measuring system, the position of each ofthe three points of reference 4 of the wheel 2. The plane is thendetermined which contains these three points of reference 4.

The points of reference 4 are measured, preferably, by means of a set-upand method as outlined in the Belgian patent application No. 9700366.

In a second variant on the method, the position of the said plane isdetermined by subjecting the wheel 2 to a revolution about the axis ofrotation thereof and passing through 180 degrees, as shown schematicallyin FIG. 2. During this rotary motion, successive positions are measuredof at least one point of reference 4. These measured positions all liealong an arc 9. Finally, the plane is determined that contains this arc9.

Also, in order to determine the correct position of the said centre ofrotation, the centre 10 of the circle on which the arc 9 lies, iscalculated. As a consequence, the said centre of rotation coincides withthis centre 10.

Next, a coordinate system 11 is defined whose first axis 12 isperpendicular to the said plane and which contains the said centre ofrotation so that this axis 12 coincides with the axis of rotation of thewheel 2. A second and third axis 13 and 14 of this coordinate system 11are perpendicular to each other and, together, from the said plane thatwas determined according to one of the variant versions as describedabove.

According to a special preferred embodiment of the method, according tothe invention, the said coordinate system 11 is then moved through aknown distance according to the axis of rotation of the wheel 2, suchthat the said second and third axes 13 and 14 constitute the mediumtransverse vertical plane 15 of the wheel 2, as shown in FIG. 3.

If the point of reference 4 of the wheel 2 is mounted on the sidesurface thereof, the coordinate system 11 should, as a consequence, bemoved, through a distance which is equal to the half the thickness ofthe wheel 2.

As and when the said actuator 1 excites the wheel 2, are measured,almost continuously, the position of the points of reference 4 of thewheel 2 and the points of reference 6 of the frame 5 by the measuringsystem 7. Based on the unequivocal relationship that exists between theposition of the points of reference 4 of the wheel 2 and those of thecoordinate system 11, is calculated the corresponding position of thelatter. In that way the correct position of the wheel 2 relative to theframe 5 is known.

Besides the calculation of translatory displacements of the wheel 2relative to the frame, this method can be also be used to determine theorientation and rotation of the wheel 2 relative to the stationaryposition or relative to the frame 5. By using, for the points ofreference 4, light-emitting diodes that produce a wide-angled beam oflight, or by using more than three points of reference, very largeexcitations of the wheel 2 can be measured. It is possible, therefore,to measure a rotation or an inclination of the wheel 2 for angles which,for example, can range between 60 and 360 degrees for the three axes ofthe coordinate system 11. Displacements relative to these axes can alsobe measured in the order of several dozens of centimeters.

In another embodiment of the method, to which the invention pertains,the position of the points of reference 4 of several wheels 2 of thesaid vehicle 3 in a state of rest relative to one another is measured asis the relative position of the points of reference 4 of the frame.

Provision is also made for a central coordinate system 16 that isreciprocating with respect to the frame 5 of the vehicle 3 and whichlies, for example, in the centre of gravity thereof. As a consequence,any deformation of the frame 5 of the vehicle 3 is determined bymeasuring the position of the various points of reference 4 of thisframe 5 in the vicinity of the wheels 2 and by calculating thedisplacement thereof relative to this central coordinate system 16 asand when these wheels are excited by the actuators 1.

In a specific embodiment of the method, to which the invention pertains,the position of the respective coordinate systems for the wheels 2 isexpressed in relative to the said central coordinate system 16. Next,according to this embodiment of the method, the relative displacement ofthe respective wheels 2, is, whenever these wheels are excited,calculated, so as to study the dynamic behaviour of the wheels 2relative to one another. Any movements of the wheels 2 can, like that,be measured relative to one another.

The invention is, of course, not limited to the method as describedabove. For example, more than three points of reference could beincorporated and measured at each wheel 2. In addition, these points ofreference 4 and 6 could, for example, consist of all manner of lightsources such as, among other things, infrared LEDs. If desired, thepoints of reference 4 and 6 could consist of a colour-coded marking,markers or, alternatively, an arbitrary identifying mark on a wheel orone the frame is used as a point of reference.

If desired, still further points of reference could be added, during themeasurement itself, on the wheel or on the frame. To that end, anadditional point of reference is fitted to the wheel or to the frame andthe position of this extra point of reference is measured and expressedrelative to the position of the other points of reference or relative toa shared system of coordinates.

In addition to that, the said measuring system could also comprise morethan three cameras and these could be, for example, linear cameras,matrix cameras or addressable cameras.

What is claimed is:
 1. A method for measuring displacement of a wheel ofa vehicle relative to the frame of the vehicle, or relative to a fixedpoint of reference when the vehicle is located on a test stand in whichthe vehicle is loaded, statically or dynamically, comprising: a.measuring each position of each of three points of reference on thewheel, said points of reference not lying in a straight line, by meansof a measuring system comprising cameras; b. measuring positions ofthree points of reference provided on the frame; and c. calculating thedisplacement of the wheel relative to the frame.
 2. The method accordingto claim 1 wherein, prior to step (a), the wheel is revolved about theaxis of rotation of the wheel, while successive positions of at leastone of the points of reference on the wheel are measured on a traced arcthrough the point of reference under consideration in which a plane isdefined which is parallel to the arc and wherein the center of thecircle on which the arc lies on which lies on the axis of rotation iscalculated, so as to determine a coordinate system, the first axis ofwhich coincides the with axis of rotation and a second and a third axislie in the said plane.
 3. The method according to claim 2 wherein thecoordinate system is displaced along the direction of the axis ofrotation over a known distance such that the plane coincides with themedian transverse vertical plane of the wheel.
 4. The method accordingto claim 2 wherein the position of the points of reference of severalwheels of the vehicle in a state of rest is determined relative to oneanother such that these points of reference can be expressed in terms ofthe same coordinate system.
 5. The method according to claim 3 whereinthe position of the points of reference of several wheels of the vehiclein a state of rest is determined relative to one another such that thesepoints of reference can be expressed in terms of the same coordinatesystem.
 6. The method according to claim 1 wherein the position of atleast three points of reference of the frame is measured, in which therelative position of the points of reference of the wheel relative tothe points of reference of the frame is calculated, such that the exactposition of the wheel is known relative to the frame.
 7. The methodaccording to claim 2 wherein the position of at least three points ofreference of the frame is measured, in which the relative position ofthe points of reference of the wheel relative to the points of referenceof the frame is calculated, such that the exact position of the wheel isknown relative to the frame.
 8. The method according to claim 3 whereinthe position of at least three points of reference of the frame ismeasured, in which the relative position of the points of reference ofthe wheel relative to the points of reference of the frame iscalculated, such that the exact position of the wheel is known relativeto the frame.
 9. The method according to claim 4 wherein the positionsof at least three points of reference of the frame is measured, in whichthe relative position of the points of reference of the wheel relativeto the points of reference of the frame is calculated, such that theexact position of the wheel is known relative to the frame.
 10. Themethod according to claim 1 wherein the wheel is loaded at a frequencybetween 10 Hz and 500 Hz.
 11. The method according to claim 2 whereinthe wheel is loaded at a frequency between 10 Hz and 500 Hz.
 12. Themethod according to claim 3 wherein the wheel is loaded at a frequencybetween 10 Hz and 500 Hz.
 13. The method according to claim 4 whereinthe wheel is loaded at a frequency between 10 Hz and 500 Hz.
 14. Themethod according to claim 6, wherein the wheel is loaded at a frequencybetween 10 Hz and 500 Hz.
 15. The method according to claim 1 whereinlinear cameras are used in the measuring system.
 16. The methodaccording to claim 2 wherein linear cameras are used in the measuringsystem.
 17. The method according to claim 3 wherein linear cameras areused in the measuring system.
 18. The method according to claim 4wherein linear cameras are used in the measuring system.
 19. The methodaccording to claim 5 wherein linear cameras are used in the measuringsystem.
 20. The method according to claim 6 wherein linear cameras areused in the measuring system.
 21. The method according to claim 1wherein infrared diodes are used for the point of reference.
 22. Themethod according to claim 2 wherein infrared diodes are used for thepoint of reference.
 23. The method according to claim 3 wherein infrareddiodes are used for the point of reference.
 24. The method according toclaim 4 wherein infrared diodes are used for the point of reference. 25.The method according to claim 5 wherein infrared diodes are used for thepoint of reference.
 26. The method according to claim 1 wherein infrareddiodes are used for the point of reference.
 27. The method according toclaim 2 wherein infrared diodes are used for the point of reference. 28.The method according to claim 2 wherein infrared diodes are used for thepoint of reference.
 29. The method according to claim 4 wherein infrareddiodes are used for the point of reference.
 30. The method according toclaim 6 wherein infrared diodes are used for the point of reference. 31.The method according to claim 10 wherein infrared diodes are used forthe point of reference.
 32. The method according to claim 15 whereininfrared diodes are used for the point of reference.